Apparatus and method for compensating image signal

Abstract

An apparatus and method for eliminating noise of a received image and compensating its sharpness is provided. A common circuit is used in a structure for eliminating noise based on a double smoothing method and a structure for making the outline sharp based on an unsharp masking method. Noise elimination and sharpness enhancement are processed for a difference signal between an original signal of the image and its low pass filtered signal, thereby compensating the original signal. Thus, an image having an improved picture quality can be provided in a product which transmits/receives or displays image data, and high competitiveness of the product can be obtained by simplifying the user interface.

What is claimed is:  
     
       1. An apparatus for compensating an image signal comprising: 
       a first filter for low pass filtering an input signal;  
       a subtractor for obtaining a difference signal between the input signal and the low pass filtered signal;  
       a noise eliminating unit for eliminating noise while preserving high frequency components of an image from the difference signal;  
       a multiplier for multiplying an output of the noise eliminating unit by a constant (α+1); and  
       an adder for adding the low pass filtered signal to the output of the multiplier.  
     
     
       2. The apparatus of  claim 1 , further comprising a delay for delaying the input signal as much as filtering time of the input signal by the first filter and outputting the delayed signal to the subtractor. 
     
     
       3. The apparatus of  claim 1 , wherein the noise eliminating unit includes: 
       an edge determinating unit for determining an edge from the difference signal;  
       a second filter for low pass filtering the difference signal; and  
       a selector selectively outputting the difference signal if the edge is determinated by the edge determinating unit while outputting the low pass filtered signal by the second filter if the edge is not determined by the edge determinating unit.  
     
     
       4. The apparatus of  claim 3 , wherein the edge determinating unit includes: 
       an edge detector for detecting an edge from the difference signal;  
       an absolute value operation unit for obtaining an absolute value of the detected edge; and  
       a comparator for comparing the edge with the absolute value with a predetermined threshold value and outputting the resultant value as a control signal.  
     
     
       5. The apparatus of  claim 3 , wherein the second filter includes a linear low pass filter or a non-linear filter. 
     
     
       6. The apparatus of  claim 3 , wherein the noise eliminating unit further includes a delay for delaying the difference signal as much as filtering time of the difference signal by the second filter and outputting the delayed signal to the selector. 
     
     
       7. The apparatus of  claim 1 , wherein the constant α of the multiplier is greater than or equal to 0. 
     
     
       8. A method for compensating an image signal comprising the steps of: 
       low pass filtering an input signal;  
       obtaining a difference signal between the input signal and the low pass filtered signal;  
       eliminating noise only while preserving high frequency components of an image from the difference signal;  
       multiplying the difference signal having no noise by a constant (α+1); and  
       adding the low pass filtered signal to the multiplied signal.  
     
     
       9. The method of  claim 8 , wherein the step of eliminating noise performs noise eliminating filtering only for a portion other than an edge. 
     
     
       10. The method of  claim 9 , wherein the step of eliminating noise includes the steps of: 
       detecting the edge from the difference signal;  
       low pass filtering the difference signal; and  
       selectively outputting the difference signal if the edge is detected while outputting the low pass filtered signal of the difference signal if the edge is not detected.  
     
     
       11. The method of  claim 10 , wherein the step of detecting the edge includes the steps of obtaining an absolute value of the detected edge from the difference signal, comparing the edge with the absolute value with a predetermined threshold value, and determining the edge if the edge with the absolute value is greater than the threshold value. 
     
     
       12. The method of  claim 8 , wherein the constant α is greater than or equal to 0.